In a steam power plant, a steam boiler is used to extract thermal energy from fuel to generate high pressure steam. The steam then flows via pipes to a steam turbine. The steam turbine converts the thermal energy of the steam into kinetic energy and uses the energy to rotate an output shaft of a generator to generate electrical power.
Several types of valves are used to control the steam during operation of a steam turbine. These include reheat stop valves, main stop valves, control valves, governors and other types of valves. The reheat and stop valves each include a clapper valve arrangement to turn steam flow on and off in the steam turbine. Referring to FIG. 1, portions of a clapper valve 10 are shown. The clapper valve 10 includes a valve disk 12 that is attached to a clapper arm 14. A rotatable clapper valve shaft 16 extends through the clapper arm 14. The shaft 16 includes a mating feature such as keys 18 that extend from the shaft 16 and into corresponding grooves in the clapper arm 14 (the keys 18 are shown spaced apart from the clapper arm 14 in FIG. 1 for purposes of illustration) such that rotation of the shaft 16 causes corresponding rotation of the clapper arm 14. In use, the clapper arm 14 may be rotated between an open position wherein the disk 12 is rotated away from a valve seat thereby opening the clapper valve 10 and enabling steam flow and a closed position wherein the disk 12 abuts against the valve seat to close the clapper valve 10 and stopping steam flow.
The clapper valve 10 is exposed to harsh conditions during operation and is periodically maintained to ensure proper operation. During maintenance, the clapper valve 10 is disassembled to enable inspection of various valve components. This includes extraction of the shaft 16 from the clapper arm 14 to determine whether bending or creep has occurred in the shaft 16. It is desirable to restrain the clapper arm 14 during removal of the shaft 16 in order to avoid damage. A plurality of axial restraints are arranged about the shaft 16 in order to restrain the clapper arm 14 while the shaft 16 is being extracted. The axial restraints are mounted to studs that extend from a clapper valve casing that houses the clapper valve 10. However, oxidation that forms on the shaft 16 during steam turbine operation renders extraction of the shaft 16 from the clapper arm 14 difficult. In particular, a large bending moment is generated during extraction of the shaft 16 that undesirably deforms one or more studs which could lead to stud damage. Further, a bushing that supports the shaft 16 along a shaft axis 20 is removed from the clapper valve casing during disassembly, thus causing the shaft 16 to be oriented or sag below the shaft axis 20 and further impedes removal of the shaft 16.